Valve gear for engine

ABSTRACT

A valve gear includes a camshaft, a first cam and a second cam that drive an intake valve or an exhaust valve, and a synchronous cam that rotates in synchronism with the first and second cams. The valve gear includes a rocker shaft, a rocker arm, and a cam follower swingably supported by the rocker shaft and that comes into contact with the synchronous cam. The valve gear includes a thruster that converts the swinging motion of the cam follower into a thrust and moves the rocker arm to a first side or a second side in the axial direction. The valve gear makes the camshaft compact, and also increases the reliability of operation at high rotations and reduces an operation sound at low rotations.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a valve gear for an engine, which switches between a plurality of cams with different cam profiles.

2. Description of the Related Art

Some recent engines mounted in vehicles are able to switch operation modes during operation. The operation modes to be switched include two operation modes having different fuel consumptions or output characteristics. Switching of the operation mode is often done using a valve gear that drives an intake valve and an exhaust valve.

A conventional valve gear capable of switching the operation mode is described in, for example, Japanese Patent Laid-Open No. 2010-249123. The valve gear disclosed in Japanese Patent Laid-Open No. 2010-249123 includes a camshaft, a rocker arm that transmits a driving force between the camshaft and an intake valve or an exhaust valve, and a driving device that switches the operation mode. The camshaft is provided with first and second cams that drive the intake valve or the exhaust valve, and an advancing and retreating cams that switch the operation mode.

The first cam and the second cam have shapes of different cam profiles. For example, the first cam has a shape with a cam nose projecting from a base circle, and the second cam has a shape of a perfect circle (for cylinder deactivation). The first and second cams or the rocker arm is movable in the axial direction of the camshaft. The first and second cams movable in the axial direction rotate integrally with the camshaft.

The valve gear described in Japanese Patent Laid-Open No. 2010-249123 presses the first and second cams or the rocker arm in the axial direction of the camshaft using the above-described advancing and retreating cams. That is, switching is performed between a first operation mode in which the rocker arm is pressed by the first cam and a second operation mode in which the rocker arm is pressed by the second cam.

The advancing cam and the retreating cam are constituted by spirally formed cam grooves and disposed side by side in the axial direction of the camshaft. The spiral of the advancing cam extends along the outer surface of the camshaft in one axial direction and the rotation direction. The spiral of the retreating cam extends along the outer surface of the camshaft in the other axial direction and the rotation direction. That is, the advancing cam and the retreating cam have shapes with spirals extending in opposite directions. This valve gear includes an advancing cam follower that selectively comes into contact with the advancing cam, and a retreating cam follower that selectively comes into contact with the retreating cam.

If the first and second cams are able to move in the axial direction, an arrangement to move the advancing cam and the retreating cam in the axial direction integrally with the first and second cams is used. In this case, the advancing cam follower, the retreating cam follower, and the rocker arm are supported by a cylinder head in a state in which they cannot move in the axial direction of the camshaft.

On the other hand, if the rocker arm is able to move in the axial direction, the advancing cam follower and the retreating cam follower are supported by a slide member that moves in the axial direction integrally with the rocker arm.

Another conventional valve gear of this type moves the rocker arm by the spring force of a helical compression spring without using the above-described advancing and retreating cams. In this valve gear, a timing of switching between the first operation mode and the second operation mode is defined by a switching timing control cam that rotates integrally with the first and second cams.

In the valve gear for an engine described in Japanese Patent Laid-Open No. 2010-249123, since the advancing cam and the retreating cam are needed on the camshaft, the total length of the camshaft increases. Recent camshafts have many functions to implement a 4-valve engine or expand capabilities. For example, the camshaft is provided with members such as gears and cams used to drive auxiliary machinery such as a high pressure fuel pump and a vacuum pump, and a rotation angle detection rotor. For this reason, to provide the advancing cam and the retreating cam on such a camshaft, the total length of the camshaft needs to be increased.

In the valve gear that moves the rocker arm in the axial direction by the spring force of a helical compression spring, a problem arises because the switching speed depends on only the spring load of the helical compression spring. In this valve gear, to correctly perform switching in a state in which the operation range of the engine is the high rotation range, a high spring load is necessary to increase the switching speed. However, if the spring load is high, a high impact load is applied to the switching portion at the time of switching, resulting in abnormal noise. The abnormal noise is not problematic in a high rotation mode with a loud engine sound. In a low rotation mode with a small engine sound, however, the abnormal noise may be unpleasant.

SUMMARY OF THE INVENTION

Preferred embodiments of the present invention provide a valve gear for an engine which provides a compact camshaft and also increases the reliability of a switching operation and reduces a switching operation sound.

According to a preferred embodiment of the present invention, a valve gear for an engine includes a camshaft rotatably supported by a cylinder head, a first cam provided on the camshaft and that drives one of an intake valve and an exhaust valve, a second cam provided on the camshaft spaced apart from the first cam in an axial direction, and that drives one of the intake valve and the exhaust valve, the second cam having a shape with a cam profile different from a cam profile of the first cam, a synchronous cam provided on the camshaft that rotates in synchronism with the first cam and the second cam, a rocker shaft parallel or substantially parallel to the camshaft, a rocker arm supported by the rocker shaft that swings and moves in the axial direction and converts a rotation of one of the first cam and the second cam into a reciprocal motion and transmits the reciprocal motion to one of the intake valve and the exhaust valve, a cam follower swingably supported by the rocker shaft and that comes into contact with the synchronous cam, and a thruster that converts the swing motion of the cam follower into a thrust in the axial direction and moves the rocker arm to one of a first side and a second side in the axial direction.

According to a preferred embodiment of the present invention, in the valve gear for the engine, the thruster preferably includes a slide portion that swings integrally with the cam follower and moves in the axial direction integrally with the rocker arm, and a switching portion supported by the cylinder head and including a first switch and a second switch, wherein the first switch and the second switch selectively come into contact with the slide portion, and the slide portion preferably includes a first inclined cam surface that receives a force in a first side thereof in the axial direction, wherein the force is generated by one of the first switch and the second switch in contact with the first inclined cam surface, and a second inclined cam surface that receives a force in a second side thereof in the axial direction, wherein the force is generated by the other of the first switch and the second switch in contact with the second inclined cam surface.

According to a preferred embodiment of the present invention, in the valve gear for the engine, a movement of the cam follower in the axial direction is preferably regulated or controlled, and the slide portion is separate from the cam follower and movable in the axial direction relative to the cam follower.

According to a preferred embodiment of the present invention, in the valve gear for the engine, each of the first switch and the second switch preferably include a pin that moves between an advancing position at which a first end comes into contact with the slide portion and a retreating position at which the first end separates from the slide portion, the second end of the pin preferably abuts against a pin cam of a moving member that moves in a direction perpendicular or substantially perpendicular to a direction in which the pin moves, and the pin cam has a shape such that when the moving member moves to a first side, the first switch moves to the advancing position and the second switch moves to the retreating position, and when the moving member moves to a second side, the first switch moves to the retreating position and the second switch moves to the advancing position.

In a preferred embodiment of the present invention, when the cam follower is pressed by the synchronous cam and swings, the thruster moves the rocker arm to a first side or a second side in the axial direction. When the rocker arm moves in the axial direction, switching is performed between a first operation mode in which the rocker arm is driven by the first cam and a second operation mode in which the rocker arm is driven by the second cam.

The synchronous cam is preferably short in the axial direction, as compared to conventional advancing and retreating cams including helical grooves.

In the valve gear, the switching speed when switching the operation mode depends on the profile (shape) and the cam rotational speed of the synchronous cam. For this reason, the switching speed changes in proportion to the cam rotational speed. As compared to a case in which the spring load of a spring member is increased when increasing the switching speed, reliability in switching at high rotations becomes high, and the operation sound at low rotations becomes small.

According to various preferred embodiments of the present invention, it is possible to provide a valve gear for an engine which provides a compact camshaft and also increases operation reliability and reduces the operation sound.

The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing an arrangement of a valve gear for an engine according to a first preferred embodiment of the present invention.

FIG. 2 is a front view showing a main portion of the valve gear according to the first preferred embodiment of the present invention in a state in which a cylinder head and a portion of a thruster are cut away.

FIG. 3 is a sectional view showing the main portion of the valve gear according to the first preferred embodiment of the present invention taken along a line III-III in FIG. 2.

FIG. 4 is a rear view showing the main portion of the valve gear according to the first preferred embodiment of the present invention in a state in which the cylinder head and a portion of the thruster are cut away.

FIG. 5A is a plan view of a cam follower of the valve gear according to the first preferred embodiment of the present invention.

FIG. 5B is a left side view of the cam follower of the valve gear according to the first preferred embodiment of the present invention.

FIG. 5C is a front view of the cam follower of the valve gear according to the first preferred embodiment of the present invention.

FIG. 5D is a right side view of the cam follower of the valve gear according to the first preferred embodiment of the present invention.

FIG. 5E is a rear view of the cam follower of the valve gear according to the first preferred embodiment of the present invention.

FIG. 5F is a bottom view of the cam follower of the valve gear according to the first preferred embodiment of the present invention.

FIG. 5G is a perspective view of the cam follower of the valve gear according to the first preferred embodiment of the present invention viewed obliquely from the lower left side.

FIG. 6A is a sectional view showing the main portion viewed from the axial direction of a camshaft so as to explain the operation of the valve gear according to the first preferred embodiment of the present invention.

FIG. 6B is a front view showing the main portion so as to explain the operation of the valve gear according to the first preferred embodiment of the present invention in a state in which a portion of the thruster is cut away.

FIG. 6C is a rear view showing the main portion so as to explain the operation of the valve gear according to the first preferred embodiment of the present invention in a state in which a portion of the thruster is cut away.

FIG. 7A is a sectional view showing the main portion viewed from the axial direction of the camshaft so as to explain the operation of the valve gear according to the first preferred embodiment of the present invention.

FIG. 7B is a front view showing the main portion so as to explain the operation of the valve gear according to the first preferred embodiment of the present invention in a state in which a portion of the thruster is cut away.

FIG. 7C is a rear view showing the main portion so as to explain the operation of the valve gear according to the first preferred embodiment of the present invention in a state in which a portion of the thruster is cut away.

FIG. 8A is a sectional view showing the main portion viewed from the axial direction of the camshaft so as to explain the operation of the valve gear according to the first preferred embodiment of the present invention.

FIG. 8B is a front view showing the main portion so as to explain the operation of the valve gear according to the first preferred embodiment of the present invention in a state in which a portion of the thruster is cut away.

FIG. 8C is a rear view showing the main portion so as to explain the operation of the valve gear according to the first preferred embodiment of the present invention in a state in which a portion of the thruster is cut away.

FIG. 9A is a sectional view showing the main portion viewed from the axial direction of the camshaft so as to explain the operation of the valve gear according to the first preferred embodiment of the present invention.

FIG. 9B is a front view showing the main portion so as to explain the operation of the valve gear according to the first preferred embodiment of the present invention in a state in which a portion of the thruster is cut away.

FIG. 9C is a rear view showing the main portion so as to explain the operation of the valve gear according to the first preferred embodiment of the present invention in a state in which a portion of the thruster is cut away.

FIG. 10 is a perspective view of the cam follower and the slide portion of a valve gear according to a second preferred embodiment of the present invention.

FIG. 11 is a rear view showing the main portion of the valve gear according to the second preferred embodiment of the present invention in a state in which a portion of a thruster is cut away.

FIG. 12 is a rear view showing the main portion of the valve gear according to the second preferred embodiment of the present invention in a state in which a portion of the thruster is cut away.

FIG. 13 is an exploded perspective view of the main portion of a valve gear according to a third preferred embodiment of the present invention.

FIG. 14 is a sectional view of the main portion of the valve gear according to the third preferred embodiment of the present invention in an operation pause state.

FIG. 15 is a front view of the valve gear according to the third preferred embodiment of the present invention in an operation pause state.

FIG. 16 is a rear view of the valve gear according to the third preferred embodiment of the present invention in an operation pause state in which the cutaway position in FIG. 14 is indicated by a line XIV-XIV.

FIG. 17 is a sectional view of the valve gear according to the third preferred embodiment of the present invention in a normal operation state.

FIG. 18 is a front view of the valve gear according to the third preferred embodiment of the present invention in a normal operation state.

FIG. 19 is a rear view of the valve gear according to the third preferred embodiment of the present invention in a normal operation state.

FIG. 20 is a perspective view of the main portion of a valve gear according to a fourth preferred embodiment of the present invention.

FIG. 21 is a side view of the valve gear according to the fourth preferred embodiment of the present invention in which the shaft main body of a camshaft is not illustrated.

FIG. 22 is a plan view of the valve gear according to the fourth preferred embodiment of the present invention in which the shaft main body of the camshaft is not illustrated.

FIG. 23 is an exploded perspective view of the main portion of the valve gear according to the fourth preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Preferred Embodiment

A valve gear for an engine according to a first preferred embodiment of the present invention will now be described in detail with reference to FIGS. 1 to 9C.

A valve gear 1 for an engine shown in FIG. 1 includes a camshaft 3 in a cylinder head 2, and a rocker arm 5 between the camshaft 3 and an intake valve 4. The rocker arm 5 is supported by a rocker shaft 6 to be swingable and movable in the axial direction.

The rocker shaft 6 is supported by the cylinder head 2 to be parallel or substantially parallel to the camshaft 3. The position of the rocker arm 5 in the axial direction is controlled by a thruster 11 to be described below.

The present preferred embodiment is applicable to both the valve gear 1 for an intake valve shown in FIG. 1 and a valve gear for an exhaust valve (not shown) that drives an exhaust valve 12. Note that the valve gear for an exhaust valve preferably has the same or similar structure as the valve gear 1 for an intake valve. Hence, in the present preferred embodiment, illustration and explanation of the valve gear for an exhaust valve are omitted.

Two intake valves 4 are provided for each cylinder. Each intake valve 4 includes a valve body 4 a that opens/closes an intake port 13 in the cylinder head 2, and a valve stem 4 b extending from the valve body 4 a into a valve gear chamber 14 in the cylinder head 2. The valve stem 4 b is movably supported on the cylinder head 2 via a valve stem guide 15. A valve spring 16 that biases the intake valve 4 in a closing direction is provided between the cylinder head 2 and the distal end of the valve stem 4 b. A cap-shaped shim 17 is provided at the distal end of the valve stem 4 b.

The intake port 13 preferably has a fork shape branching in the cylinder head 2. The upstream end of the intake port 13 opens to a side of the cylinder head 2, and the downstream end of the intake port 13 opens to a combustion chamber 18. A spark plug 19 is provided at the center of the combustion chamber 18. As shown in FIG. 1, the spark plug 19 is provided at a position different from a cylinder axis C when viewed from the axial direction of the camshaft 3.

The camshaft 3 rotates when the rotation of a crankshaft (not shown) is transmitted via a transmission mechanism. The camshaft 3 according to the present preferred embodiment includes a camshaft main body 21 preferably with a rod shape, and a plurality of cams provided on the camshaft main body 21, as shown in FIG. 2. The plurality of cams includes a first cam 22 and a second cam 23 which are provided for each intake valve 4, and a synchronous cam 24 located between the two sets of first cams 22 and second cams 23.

The first cam 22 and the second cam 23 drive the intake valve 4. The second cam 23 has a cam profile different from that of the first cam 22, and has a shape the provides a different valve lift amount in the present preferred embodiment. In addition, the second cam 23 is provided on the camshaft 3 at a position spaced apart from the first cam 22 in the axial direction. As shown in FIG. 3, the first cam 22 and the second cam 23 include base circle portions 22 a and 23 a and nose portions 22 b and 23 b, respectively. Each of the base circle portions 22 a and 23 a preferably has a columnar shape and is located on the same axis as the camshaft main body 21, and has a size in which the valve lift amount of the intake valve 4 becomes 0.

Each of the nose portions 22 b and 23 b has a shape projecting from a corresponding one of the base circle portions 22 a and 23 a outward in the radial direction by a predetermined projecting amount so as to have a mountain-shaped section. The projecting amount of the nose portion 22 b of the first cam 22 is larger than the projecting amount of the nose portion 23 b of the second cam 23.

The synchronous cam 24 drives the thruster 11 (to be described below), and includes a base circle portion 24 a and a nose portion 24 b. The synchronous cam 24 rotates in synchronism with valve driving cams including the first cams 22 and the second cams 23. The nose portion 24 b of the synchronous cam 24 is located at a position different from the positions of the nose portions 22 b and 23 b of the first cam 22 and the second cam 23 in the rotation direction of the camshaft 3.

The rocker arm 5 is substantially U-shaped in a plan view including two arm main bodies 25 that each convert the rotation of the first cam 22 or the second cam 23 into a reciprocal motion and transmit it to the intake valve 4, and a connector 26 that connects the swing ends of the arm main bodies 25 to each other. The rocker shaft 6 extends through the proximal portions of the two arm main bodies 25.

A presser 27 that presses the intake valve 4 is provided at each swing end of the rocker arm 5, as shown in FIG. 2. The presser 27 is larger than the shim 17 in the axial direction of the rocker shaft 6. For this reason, the presser 27 of the rocker arm 5 never disengages from the shim 17 even if the rocker arm 5 moves in the axial direction of the rocker shaft 6.

As shown in FIG. 4, the two arm main bodies 25 are spaced apart at a predetermined interval in the axial direction of the rocker shaft 6. A slider 31 that defines a portion of the thruster 11 is inserted between the two arm main bodies 25.

As shown in FIG. 3, the thruster 11 includes a slide portion 32 with the above-described slider 31, and a switching portion 33 provided at a position adjacent to the slide portion 32.

The slide portion 32 includes the slider 31 through which the rocker shaft 6 extends, and a plurality of functional portions (to be described below in detail) provided on the slider 31. As shown in FIG. 4, the slider 31 is inserted between the two proximal portions of the two arm main bodies 25 in a state in which it is in slidable contact with the proximal portions, and is also supported by the rocker shaft 6 to be pivotal and movable in the axial direction. When the slider 31 moves in the axial direction of the rocker shaft 6, the rocker arm 5 integrally moves in the same direction as the slider 31.

A cam follower 34 that contacts the synchronous cam 24 is integral with the slider 31 in the present preferred embodiment. As shown in FIG. 3, the cam follower 34 preferably has a lever shape extending in a direction crossing the longitudinal direction of the rocker arm 5 as viewed from the axial direction of the rocker shaft 6. The distal end of the cam follower 34 extends up to a position adjacent to the camshaft 3. When the camshaft 3 rotates in a state in which the cam follower 34 is close to the camshaft 3, the synchronous cam 24 presses the cam follower 34, and the cam follower 34 and the slider 31 swing about the rocker shaft 6 in a swinging direction indicated by an arrow A in FIGS. 5B to 5D.

As shown in FIG. 4, an axial length of the synchronous cam 24 according to the present preferred embodiment is larger than the width (the width in the horizontal direction in FIG. 4, or the width in the axial direction of the rocker shaft 6) of the cam follower 34. This prevents the cam follower 34 from disengaging from the synchronous cam 24 when the cam follower 34 moves in the axial direction together with the slider 31.

The synchronous cam 24 has a shape that presses the cam follower 34 when the rocker arm 5 contacts the base circle portion 22 a of the first cam 22 or the base circle portion 23 a of the second cam 23, as shown in FIG. 9A. In other words, when the intake valve 4 is closed, the cam follower 34 is pressed by the synchronous cam 24 and swings.

The plurality of functional portions provided on the slider 31 include a first inclined cam surface 35 (see FIG. 4) and a second inclined cam surface 36, which are located on the slider 31 on the opposite side of the cam follower 34, and a first concave groove 37 (see FIG. 2) and a second concave groove 38.

As shown in FIGS. 5B and 5D, the first inclined cam surface 35 and the second inclined cam surface 36 are provided on a convex portion 39 of the slider 31. The convex portion 39 projects in a direction different from the direction in which the cam follower 34 projects from the slider 31. In the assembled state shown in FIG. 3, the convex portion 39 according to the present preferred embodiment projects in a direction opposite to the direction in which the rocker arm 5 extends. As shown in FIG. 5C, the convex portion 39 has a mountain-shaped section projecting to the opposite side of the cam follower 34. The first inclined cam surface 35 and the second inclined cam surface 36 are provided on the surface (lower surface) of the convex portion 39 on the opposite side of the cam follower 34.

The first inclined cam surface 35 and the second inclined cam surface 36 according to the present preferred embodiment are preferably flat surfaces that are inclined in directions opposite to each other in the axial direction of the rocker shaft 6, as shown in FIGS. 4 and 5B to 5G. As shown in FIG. 5C, the first inclined cam surface 35 and the second inclined cam surface 36 extend from the center of the convex portion 39 in the axial direction of the rocker shaft 6 to a first end and a second end. The first inclined cam surface 35 is inclined to gradually lower from the center of the convex portion 39 to the first end.

The second inclined cam surface 36 is inclined to gradually lower from the center of the convex portion 39 to the second end. Note that the first inclined cam surface 35 and the second inclined cam surface 36 may have concave curved surfaces, although not illustrated.

As shown in FIG. 5F, the first concave groove 37 and the second concave groove 38 are located at an end of the slider 31 on the opposite side of the cam follower 34 at positions adjacent to the first inclined cam surface 35 and the second inclined cam surface 36 in the longitudinal direction of the convex portion 39. The first concave groove 37 and the second concave groove 38 are side by side in the axial direction of the rocker shaft 6, and extend in a direction perpendicular or substantially perpendicular to the axial direction of the rocker shaft 6.

As shown in FIGS. 3 and 4, the switching portion 33 of the thruster 11 includes a first pin 41 facing the first inclined cam surface 35, a second pin 42 facing the second inclined cam surface 36, a moving member 43 in contact with the pins 41 and 42, and a third pin 44 to be engageably inserted in the first concave groove 37 or second concave groove 38. In the present preferred embodiment, the first pin 41 corresponds to a first switch, and the second pin 42 corresponds to a second switch.

As shown in FIG. 3, the first pin 41 and the second pin 42 are supported by the cylinder head 2 to be movable in the longitudinal direction in a state in which they are parallel or substantially parallel to the valve stem 4 b of the intake valve 4. As shown in FIG. 4, the first pin 41 and the second pin 42 are provided at predetermined positions spaced apart from each other at a predetermined interval in the axial direction of the rocker shaft 6. The predetermined positions are positions associated with the first inclined cam surface 35 and the second inclined cam surface 36.

As shown in FIG. 6C, the first pin 41 is provided at a position facing the projecting end of the first inclined cam surface 35 in a state in which the slider 31 has moved to the first end with the first inclined cam surface 35 in the axial direction of the rocker shaft 6. The projecting end is a portion near the top defined by the first inclined cam surface 35 and the second inclined cam surface 36.

On the other hand, as shown in FIG. 4, the second pin 42 is provided at a position facing the projecting end of the second inclined cam surface 36 in a state in which the slider 31 has moved to the second end with the second inclined cam surface 36 in the axial direction of the rocker shaft 6.

The first pin 41 and the second pin 42 move between an advancing position to advance toward the slider 31 and a retreating position to retreat in a direction opposite to the slider 31. When the slider 31 swings integrally with the cam follower 34, the first pin 41 and the second pin 42 that advance to the advancing position are brought into contact with the first inclined cam surface 35 or the second inclined cam surface 36. In a state in which the first pin 41 and the second pin 42 move to the retreating position, the movement of the first inclined cam surface 35 or the second inclined cam surface 36 is not impeded even if the slider 31 swings. FIG. 4 shows a state in which the first pin 41 is located at the advancing position, and the second pin 42 is located at the retreating position. The advancing position and the retreating position are controlled by the moving member 43 that comes into contact with the first pin 41 and the second pin 42.

The moving member 43 preferably has a columnar shape and is movably fitted in an oil hole 45 of the cylinder head 2. The oil hole 45 is parallel or substantially parallel to the rocker shaft 6. For this reason, the moving member 43 moves in a direction perpendicular or substantially perpendicular to the direction in which the first pin 41 and the second pin 42 move.

The moving member 43 according to the present preferred embodiment includes a piston that moves in the oil hole 45. A helical compression spring 46 is inserted on a first end (the left side in FIG. 4) of the oil hole 45. The helical compression spring 46 biases the moving member 43 to the second end of the oil hole 45. Note that both the spring force of the helical compression spring 46 and an oil pressure may be applied to one end of the moving member 43. The end of the moving member 43 close to the helical compression spring 46 will simply be referred to as a first end and the end on the opposite side as the second end hereinafter.

The second end of the oil hole 45 is connected to an oil pressure supply device (not shown). Hence, an oil pressure propagated from the oil pressure supply device is applied to the second end (the end on the right side in FIG. 4) of the moving member 43.

A first pin cam 47 that moves the first pin 41 between the advancing position and the retreating position and a second pin cam 48 that moves the second pin 42 between the advancing position and the retreating position are provided in the moving member 43. The cams 47 and 48 preferably symmetrical to each other with respect to a plane of symmetry defined by a virtual plane perpendicular or substantially perpendicular to the axis of the moving member 43.

The first pin cam 47 and the second pin cam 48 include curved surfaces extending from concave portions 49 and 50 in which the ends of the first pin 41 and the second pin 42 are inserted to the outer surface of the moving member 43. The first pin 41 and the second pin 42 are inserted in the concave portions 49 and 50 and thus located at the retreating position.

The first pin cam 47 is provided at a first end of the moving member 43. When the moving member 43 moves to a first end (the left side in FIG. 6C) of the oil hole 45 from a state in which the first pin 41 is located in the concave portion 49 and at the retreating position (see FIG. 6C), the first pin cam 47 pushes the first pin 41 out of the concave portion 49 and places the first pin 41 on the outer surface of the moving member 43, as shown in FIG. 7C. The first pin 41 that has moved to the advancing position comes into contact with the first inclined cam surface 35 when the slider 31 swings.

The second pin cam 48 is provided at the second end of the moving member 43. The second pin cam 48 has a shape that moves the second pin 42 to the advancing position (see FIG. 6C) when the moving member 43 moves to the second end (the right side in FIG. 4) from a state in which the second pin 42 is located in the concave portion 50 and at the retreating position (see FIG. 4). The second pin 42 that has moved to the advancing position comes into contact with the second inclined cam surface 36 when the slider 31 swings.

That is, the first pin 41 and the second pin 42 selectively come into contact with the slide portion 32 (slider 31) when the moving member 43 moves to the first end or the second end.

The first pin cam 47 and the second pin cam 48 are arranged such that, when one of the first pin 41 and the second pin 42 is located at the advancing position, the other of the first pin 41 and the second pin 42 moves to the retreating position. That is, when the moving member 43 moves to a first end, the first pin 41 moves to the advancing position, and the second pin 42 returns to the retreating position, as shown in FIG. 7C. In addition, when the moving member 43 moves to the second end that is the other side in the longitudinal direction, the first pin 41 returns to the retreating position, and the second pin 42 moves to the advancing position, as shown in FIG. 6C.

As shown in FIGS. 2 and 3, the third pin 44 is faces the first concave groove 37 or the second concave groove 38 of the slider 31 and is movably supported by the cylinder head 2 parallel or substantially parallel to the valve stem 4 b of the intake valve 4. The direction in which the third pin 44 moves is the direction parallel or substantially parallel to the valve stem 4 b of the intake valve 4. The distal end of the third pin 44 preferably has a hemispherical shape.

In addition, the third pin 44 is pressed against the first concave groove 37 or the second concave groove 38 by the spring force of a helical compression spring 51 provided between the third pin 44 and the cylinder head 2. For this reason, the slider 31 is biased by the spring force of the helical compression spring 51 in a direction in which the cam follower 34 separates from the camshaft 3 about the rocker shaft 6. When biased by the spring force of the helical compression spring 51, the slider 31 swings in the swinging direction A about the rocker shaft 6 until the first inclined cam surface 35 or the second inclined cam surface 36 comes into contact with the first pin 41 or the second pin 42. For this reason, the slider 31 and the cam follower 34 are maintained in a state in which the first inclined cam surface 35 or the second inclined cam surface 36 is in contact with the first pin 41 or the second pin 42 when the cam follower 34 is not pressed by the synchronous cam 24.

The first concave groove 37 and the second concave groove 38 each preferably include a V-shaped section, as shown in FIG. 2. For this reason, for example, if the slider 31 moves in a direction (the right side in FIG. 2) opposite to the second concave groove 38 in a state in which the third pin 44 engages with the first concave groove 37, as shown in FIG. 2, the inclined side wall of the first concave groove 37 pushes the third pin 44, and the third pin 44 moves in a direction opposite to the slider 31 against the spring force of the helical compression spring 51.

Then, the third pin 44 moves across the top that defines the boundary between the first concave groove 37 and the second concave groove 38 and enters the second concave groove 38. The third pin 44 that has entered the second concave groove 38 presses the side wall of the second concave groove 38 by the spring force of the helical compression spring 51. Since this side wall is inclined as well, the movement of the slider 31 is assisted by the spring force of the helical compression spring 51. The slider 31 stops when the third pin 44 advances to the deepest point of the second concave groove 38. The operation of the third pin 44 is performed similarly even if the slider 31 moves in a direction opposite to the above-described direction.

In a state in which the third pin 44 is inserted in the first concave groove 37, as shown in FIG. 2, the slider 31 and the rocker arm 5 according to the present preferred embodiment are located at a first position at which the rocker arm 5 contacts the first cams 22. When the rocker arm 5 is located at the first position, a first operation mode in which the intake valve 4 is driven by the first cams 22 is performed.

In a state in which the third pin 44 is inserted in the second concave groove 38, as shown in FIG. 6B, the slider 31 and the rocker arm 5 are located at a second position at which the rocker arm 5 contacts the second cams 23. When the rocker arm 5 is located at the second position, a second operation mode in which the intake valve 4 is driven by the second cams 23 is performed.

The operation of the valve gear 1 will be described next with reference to FIGS. 6A to 9C. An operation performed when shifting from the second operation mode in which the intake valve 4 is driven by the second cams 23 to the first operation mode will be explained here.

When the second operation mode is performed, the rocker arm 5 is located at a position where it is pressed by the second cams 23, as shown in FIG. 6A, and the third pin 44 is inserted in the second concave groove 38, as shown in FIG. 6B. The moving member 43 moves to the second end, as shown in FIG. 6C. The first pin 41 is located at the retreating position, and the second pin 42 is located at the advancing position.

When switching from the second operation mode to the first operation mode, the moving member 43 is moved from the second end to the first end, as shown in FIG. 7C. When the moving member 43 moves from the second end to the first end, the first pin 41 is located on the outer surface of the moving member 43 and moves to the advancing position to press the first inclined cam surface 35. When the first inclined cam surface 35 is pressed by the first pin 41, as shown in FIG. 7A, the slider 31 and the cam follower 34 swing in a direction (counterclockwise in FIG. 7A) opposite to the swinging direction A, and the cam follower 34 approaches the camshaft 3. At this time, the movement (movement in the axial direction of the rocker shaft 6) of the slider 31 is controlled by the third pin 44. Additionally, at this time, the concave portion 50 of the moving member 43 is located at a position facing the second pin 42.

When the camshaft 3 rotates in this state, the cam follower 34 is pressed by the synchronous cam 24 in a state in which the rocker arm 5 is in contact with the base circle portions 23 a of the second cams 23, and the slider 31 integrally swings in the swinging direction A with the cam follower 34, as shown in FIG. 8A. When the slider 31 swings, the projecting end of the first inclined cam surface 35 is pressed against the first pin 41, as shown in FIG. 8C. In a state in which the first pin 41 is located at the advancing position, the first pin 41 cannot move (retreat) even if the slider 31 swings to bring the first inclined cam surface 35 into contact with the first pin 41.

As described above, when the projecting end of the first inclined cam surface 35 is pressed against the first pin 41, the first inclined cam surface 35 receives a thrust. The direction in which the thrust acts is the direction in which the low portion of the first inclined cam surface 35 approaches the first pin 41. As a result, the slider 31 integrally moves to the second end (the right side in FIG. 8C) with the rocker arm 5. When the slider 31 starts moving, the third pin 44 is pressed by the side wall of the second concave groove 38 and retreats against the spring force of the helical compression spring 51, as shown in FIG. 8B.

As shown in FIGS. 9A and 9B, the third pin 44 moves from the second concave groove 38 into the first concave groove 37 during a time until the top (the distal end portion where the nose portion 24 b projects most) of the synchronous cam 24 presses the cam follower 34. When the top of the synchronous cam 24 passes through the cam follower 34, the thrust disappears because the cam follower 34 is not pressed by the synchronous cam 24. Note that when the slider 31 moves in accordance with the swing motion of the cam follower 34, the second pin 42 is pressed by the second inclined cam surface 36 and returns to the retreating position.

When the top of the synchronous cam 24 passes through the cam follower 34, the third pin 44 is in a state in which it presses the side wall of the first concave groove 37. For this reason, although the first inclined cam surface 35 separates from the first pin 41, the side wall of the first concave groove 37 is pressed by the third pin 44 according to the spring force of the helical compression spring 51, and the slider 31 further moves to the second end. The slider 31 stops when the third pin 44 advances to the deepest point of the first concave groove 37. When the slider 31 stops in this way, the rocker arm 5 is located at the first position at which the rocker arm 5 contacts the first cams 22, as shown in FIGS. 9B and 9C, and the operation mode shifts to the first operation mode in which the intake valve 4 is driven by the first cams 22.

A shift from this operation mode to the second operation mode in which the intake valve 4 is driven by the second cams 23 is made by moving the moving member 43 to the second end (the right side in FIG. 9C) from a state shown in FIG. 9C. When the moving member 43 moves in this way, the second pin 42 moves to the advancing position, and the cam follower 34 comes into contact with the synchronous cam 24. The cam follower 34 swings, the second pin 42 comes into contact with the second inclined cam surface 36 to generate a thrust, and the slider 31 moves. At this time, the slider 31 moves to the left side in FIG. 9C from the position shown in FIG. 9C to the position shown in FIG. 6C. In addition, the first inclined cam surface 35 presses the first pin 41 in accordance with the movement of the slider 31, and the first pin 41 returns to the retreating position.

The synchronous cam 24 used in the valve gear 1 for an engine is preferably short in the axial direction, as compared to conventional advancing and retreating cams including helical grooves. This means that the camshaft 3 is short. In addition, the synchronous cam 24 is able to be made by the same manufacturing method as the first cam 22 and the second cam 23. That is, the synchronous cam 24 is able to be made using a cam processing machine used to make the first cam 22 and the second cam 23.

In the valve gear 1 according to the present preferred embodiment, the switching speed when switching the operation mode is determined depending on the profile (shape) and the cam rotational speed of the synchronous cam 24. For this reason, the switching speed changes in proportion to the cam rotational speed. As compared to a case in which the spring load of a spring member is increased when increasing the switching speed, reliability in switching in a high rotation state becomes high, and the operation sound in a low rotation state becomes small.

In the valve gear 1 according to the present preferred embodiment, the main operation sound generated when switching the operation mode includes the sound of friction between the first inclined cam surface 35 or the second inclined cam surface 36 and the first pin 41 or the second pin 42, and the sound of friction between the third pin 44 and the slider 31. Such a sound is smaller than the sound of collision between metal members.

Hence, according to the present preferred embodiment, it is possible to provide a valve gear for an engine, in which the camshaft 3 is made compact and at low cost and also increases the reliability of the operation and reduces the operation sound.

The slide portion 32 of the thruster 11 according to the present preferred embodiment includes the first inclined cam surface 35 and the second inclined cam surface 36, and moves in the axial direction of the rocker shaft 6 when the cam follower 34 swings to press the cam surface 35 or 36 against the first pin 41 or the second pin 42.

For this reason, the thruster 11 according to the present preferred embodiment is small and has a simple structure, as compared to a case in which a link or gear is used to convert the swinging motion of the cam follower 34 into a thrust in the axial direction. Hence, according to the present preferred embodiment, it is possible to provide a valve gear for an engine that has a small size at a reduced cost.

As for the first pin 41 and the second pin 42 according to the present preferred embodiment, when one pin is located at the advancing position, the other pin moves to the retreating position. Hence, according to the present preferred embodiment, since the first pin 41 and the second pin 42 never simultaneously move to the advancing position, it is possible to provide a valve gear for an engine in which the thruster 11 has high operation reliability.

Second Preferred Embodiment

A valve gear for an engine according to a second preferred embodiment of the present invention will be described in detail with reference to FIGS. 10 to 12. The same reference numerals as in FIGS. 1 to 9C denote the same or similar members in FIGS. 10 to 12, and a detailed description thereof will appropriately be omitted.

A valve gear 61 (see FIG. 11) for an engine according to the present preferred embodiment is different from the valve gear 1 described in the first preferred embodiment only in the structures of a cam follower 34 and a slider 31. The rest of the arrangement of the valve gear 61 is preferably the same as in the valve gear 1 described in the first preferred embodiment.

As shown in FIG. 10, the cam follower 34 according to the present preferred embodiment is separate from the slider 31. A proximal portion 34 a of the cam follower 34 is inserted into a concave portion 62 of the slider 31. A through hole 63 that receives a rocker shaft 6 (see FIG. 11) is provided in the proximal portion 34 a. The rocker shaft 6 passes through the through hole 63 and two through holes 64 at the two ends of the slider 31.

A swing end 34 b of the cam follower 34 is swingably inserted into a concave groove 66 of a stopper 65 fixed to a cylinder head (not shown). Each side wall of the concave groove 66 contacts the cam follower 34 when the cam follower 34 moves in the axial direction of the rocker shaft 6. That is, movement of the cam follower 34 according to the present preferred embodiment is regulated or controlled by the side walls of the concave groove 66 and, therefore, cannot move in the axial direction of the rocker shaft 6.

To allow the slider 31 to move relative to the cam follower 34 in the axial direction of the rocker shaft 6, the concave portion 62 of the slider 31 is longer than the cam follower 34 by a predetermined length in the axial direction of the rocker shaft 6. The predetermined length is a length that allows the slider 31 to move relative to the cam follower 34 between a position at which a rocker arm 5 contacts first cams 22, as shown in FIG. 11, and a position at which the rocker arm 5 contacts second cams 23, as shown in FIG. 12.

The proximal portion 34 a of the cam follower 34 is provided with a first convex portion 67 and a second convex portion 68 to regulate or control its swinging motion relative to the slider 31. The first convex portion 67 and the second convex portion 68 are provided at positions spaced apart to one side and the other side in the radial direction of the rocker shaft 6. The first convex portion 67 comes into contact with a pressure receiving portion 69 of the slider 31, and the second convex portion 68 comes into contact with a transmitting portion 70 of the slider 31. That is, when the cam follower 34 is pressed by a synchronous cam 24 and swings, the pressing force is transmitted from the cam follower 34 to the slider 31 via the contact portion between the first convex portion 67 and the pressure receiving portion 69. When the slider 31 is pressed by a third pin 44 and swings, the pressing force is transmitted from the slider 31 to the cam follower 34 via the contact portion between the second convex portion 68 and the transmitting portion 70.

In the valve gear 61 according to the present preferred embodiment, even if the slider 31 moves in the axial direction of the rocker shaft 6, the position of the cam follower 34 does not change. For this reason, as compared to a case in which the cam follower 34 moves in the axial direction of the rocker shaft 6, the synchronous cam 24 that presses the cam follower 34 is short in the axial direction. Hence, according to the present preferred embodiment, since the location of the synchronous cam 24 on a camshaft 3 is narrow, the camshaft 3 is able to be shorter.

Third Preferred Embodiment

A valve gear according to a third preferred embodiment the present invention is shown in FIGS. 13 to 19. The same reference numerals as in FIGS. 1 to 9C denote the same or similar members in FIGS. 13 to 19, and a detailed description thereof will appropriately be omitted.

A valve gear 71 for an engine according to the present preferred embodiment is different from the valve gear 1 described in the first preferred embodiment in the structures of a camshaft 3, a rocker arm 5, a cam follower 34, and a thruster 11. As for the cam follower 34 according to the present preferred embodiment, the movement in the axial direction is regulated or controlled, as in a case of the second preferred embodiment. The rest of the arrangement of the valve gear 71 is preferably the same as in the valve gear 1 described in the first preferred embodiment.

As shown in FIG. 15, two first cams 22 of the camshaft 3 according to the present preferred embodiment are located at positions adjacent to a synchronous cam 24. Second cams 23 are located at positions that sandwich the first cams 22 from both sides. As shown in FIG. 14, each second cam 23 has no nose portion and includes only a base circle portion 23 a. That is, the valve gear 71 according to the present preferred embodiment switches between a first operation mode in which an intake valve 4 is driven by the first cams 22 and a second operation mode in which the intake valve 4 does not open.

As shown in FIG. 13, the rocker arm 5 according to the present preferred embodiment is provided for each intake valve 4 (see FIG. 15). That is, the rocker arm 5 according to the present preferred embodiment includes only an arm main body 25, and includes no connector 26 included in the first preferred embodiment.

A slide portion 32 of the thruster 11 according to the present preferred embodiment includes a first slider 72 and a second slider 73, which are separated from the cam follower 34, and a plurality of functional portions provided on each of the sliders 72 and 73. The first slider 72 and the second slider 73 are preferably symmetrical to each other with respect to a plane of symmetry defined by a virtual plane perpendicular or substantially perpendicular to the axis of the rocker arm 5. Through holes 74 that receive the rocker shaft 6 (see FIG. 15) are provided in the first slider 72 and the second slider 73. The first slider 72 and the second slider 73 are supported by a rocker shaft 6 to be pivotal and movable in the axial direction.

The functional portions provided on the first slider 72 and the second slider 73 include a first inclined cam surface 35 and a second inclined cam surface 36 (see FIG. 16), and a first concave groove 37 and a second concave groove 38 (see FIG. 15). In the present preferred embodiment, inclined cam surfaces and concave grooves located on lateral portions of the first slider 72 and the second slider 73 close to each other will be referred to as the first inclined cam surfaces 35 and the first concave grooves 37 for convenience. In addition, inclined cam surfaces and concave grooves located on the other lateral portion of the first slider 72 and the second slider 73 will be referred to as the second inclined cam surfaces 36 and the second concave grooves 38.

As shown in FIG. 13, an outer concave portion 75 that holds the rocker arm 5 and an inner concave portion 77 that receives a boss 76 of the cam follower 34 (to be described below) are provided in each of the first slider 72 and the second slider 73 according to the present preferred embodiment.

The outer concave portion 75 has a shape that allows the rocker arm 5 to swing and regulates or controls the movement of the rocker arm 5 in the axial direction relative to the first slider 72 and the second slider 73.

The rocker arms 5 are swingably supported by the first slider 72 and the second slider 73 via the rocker shaft 6 by inserting the rocker shaft 6 into the through holes 74 of the sliders 72 and 73 and shaft holes 78 of the rocker arms 5 in a state in which the proximal portions are inserted in the outer concave portions 75. The rocker arm 5 supported by the first slider 72 moves in the axial direction of the rocker shaft 6 together with the first slider 72. The rocker arm 5 supported by the second slider 73 moves in the axial direction of the rocker shaft 6 together with the second slider 73.

As shown in FIG. 13, the cam follower 34 according to the present preferred embodiment includes the cylindrical boss 76 through which the rocker shaft 6 passes, a lever 79 extending from the boss 76 in the radial direction of the rocker shaft 6, and a first connector 80 and a second connector 81 which extend from the lever 79 in the axial direction of the rocker shaft 6. The boss 76, the lever 79, the first connector 80, and the second connector 81 are preferably integral, for example, and may be formed by integral molding.

The hollow portion of the boss 76 has a shape that allows the rocker shaft 6 to be rotatably fitted therein. The length of the boss 76 in the axial direction is larger than the width (the width in the axial direction of the rocker shaft 6) of the lever 79. The lever 79 is located at the center of the boss 76 in the axial direction. For this reason, the two ends of the boss 76 project from the lever 79 in the axial direction. As shown in FIG. 18, the projecting portions are located in the inner concave portions 77 of the first slider 72 and the second slider 73 when the first slider 72 and the second slider 73 approach each other.

The first connector 80 and the second connector 81 regulate or control the swinging motion of the cam follower 34 relative to the sliders 72 and 73, and are located at different positions in the swinging direction of the cam follower 34. As shown in FIG. 14, the first connector 80 is located on the downstream side of the lever 79 in the swinging direction of the cam follower 34. Here, the downstream side is the downstream side in a swinging direction A when the cam follower 34 is pressed by the synchronous cam 24 and swings. The first connector 80 comes into contact with pressure receiving portions 82 provided on the first slider 72 and the second slider 73 from the upstream side in the above-described swinging direction. That is, when the cam follower 34 is pressed by the synchronous cam 24 and swings, the pressing force is transmitted from the cam follower 34 to the first slider 72 and the second slider 73 via the contact portions between the first connector 80 and the pressure receiving portions 82.

The second connector 81 is located on the upstream side of the first connector 80 in the swinging direction A. The second connector 81 comes into contact with transmitting portions 83 provided on the first slider 72 and the second slider 73 from the downstream side in the swinging direction A. That is, when the first slider 72 and the second slider 73 are pressed by third pins 44 (to be described below) and swing, the pressing force is transmitted from the first slider 72 and the second slider 73 to the cam follower 34 via the contact portions between the second connector 81 and the transmitting portions 83.

As shown in FIG. 16, each of the first connector 80 and the second connector 81 has a length to contact the pressure receiving portion 82 or transmitting portion 83 in a state in which the first slider 72 and the second slider 73 move to maximum moving positions in a direction in which they are separated from each other. Hence, the cam follower 34, the first slider 72, and the second slider 73 always integrally swing.

As shown in FIGS. 15 and 16, a switching portion 33 of the thruster 11 according to the present preferred embodiment includes a first pin 41 and a second pin 42 for each slider, one moving member 43 including first pin cams 47 and second pin cams 48 that drive the pins 41 and 42, and a third pin 44 for each slider.

The first pin 41 faces the first inclined cam surface 35, and the second pin 42 faces the second inclined cam surface 36.

The first pin cam 47 and the second pin cam 48 of the moving member 43 are provided for each slider. The first pin cam 47 and the second pin cam 48 according to the present preferred embodiment include an arrangement to move the first slider 72 and the second slider 73 in directions opposite to each other. More specifically, when the moving member 43 moves from the position on the second end shown in FIG. 19 to the position on the first end shown in FIG. 16, the first pin cam 47 moves the first pin 41 from the retreating position to the advancing position.

When the moving member 43 moves from the position on the first end shown in FIG. 16 to the position on the second end shown in FIG. 19, the second pin cam 48 moves the second pin 42 from the retreating position to the advancing position. In the present preferred embodiment as well, the first pin cam 47 and the second pin cam 48 include an arrangement such that, when one of the first pin 41 and the second pin 42 is located at the advancing position, the other pin moves to the retreating position.

In the valve gear 71 for an engine according to the present preferred embodiment, when the moving member 43 moves from the position on the first end shown in FIG. 16 to the position on the second end shown in FIG. 19, the second pin 42 moves from the retreating position to the advancing position, and the first slider 72 and the second slider 73 are moved to positions at which they are in contact with each other, as shown in FIG. 19, by a thrust acting on the second inclined cam surfaces 36. At this time, the third pins 44 move from the first concave grooves 37 of the first slider 72 and the second slider 73 into the second concave grooves 38.

When the first slider 72 and the second slider 73 move in this way, the rocker arms 5 contact the first cams 22, and the intake valves 4 are driven by the first cams 22, as shown in FIGS. 17 and 18.

On the other hand, when the moving member 43 moves from the position on the second end shown in FIG. 19 to the position on the first end shown in FIG. 16, the first pin 41 moves to the advancing position, and the first slider 72 and the second slider 73 are moved in directions in which they are separated from each other, as shown in FIG. 16, by a thrust acting on the first inclined cam surfaces 35. At this time, the third pins 44 move from the second concave grooves 38 of the sliders 72 and 73 into the first concave grooves 37. When the first slider 72 and the second slider 73 move in this way, the rocker arms 5 contact the second cams 23, and the intake valves 4 are maintained in the closed state, as shown in FIGS. 14 and 15.

For this reason, according to the present preferred embodiment, it is possible to provide a valve gear for an engine that is able to switch between the first operation mode in which the intake valves 4 operate and the second operation mode in which the intake valves 4 are at rest.

Fourth Preferred Embodiment

A slider and a cam follower in a valve gear according to a fourth preferred embodiment of the present invention is shown in FIGS. 20 to 23. The same reference numerals as in FIGS. 1 to 12 denote the same or similar members in FIGS. 20 to 23, and a detailed description thereof will appropriately be omitted.

A valve gear 91 for an engine according to the present preferred embodiment is different from the valve gear 61 described in the second preferred embodiment (FIGS. 10 to 12) in the structures of a cam follower 34 and a slider 31. The rest of the arrangement of the valve gear 91 is preferably the same as in the valve gear 61 described in the second preferred embodiment. As for the cam follower 34 according to the present preferred embodiment, the movement in the axial direction is regulated or controlled by a stopper 65 (see FIG. 21). Two rocker arms 5 per cylinder are located on both sides of a slider 92 (see FIG. 23) according to the present preferred embodiment, and are swingably supported by one tubular shaft 93 together with the slider 92.

The tubular shaft 93 is inserted into shaft holes 94 of the two rocker arms 5 and through holes 64 of the slider 92 and extends through these members. A rocker shaft 6 is fitted in the hollow portion of the tubular shaft 93. The tubular shaft 93 is supported by the rocker shaft 6 to be rotatable and movable in the axial direction. The two rocker arms 5 and the slider 92 are mounted on the tubular shaft 93 in a state in which they are in contact with each other in the axial direction of the tubular shaft 93. Circlips 95 are attached to the two ends of the tubular shaft 93 in a state in which the circlips 95 are in contact with the rocker arms 5. That is, the two rocker arm 5, the slider 92, and the tubular shaft 93 integrally move relative to the rocker shaft 6 in the axial direction.

Each rocker arm 5 according to the present preferred embodiment includes a roller 96 that contacts a first cam 22 or a second cam 23.

The slider 92 according to the present preferred embodiment is different from the slider 31 described in the second preferred embodiment in the location of a convex portion 39 including a first inclined cam surface 35, a second inclined cam surface 36, a first concave groove 37, and a second concave groove 38. The convex portion 39 extends almost parallel or substantially parallel to a cylinder axis C (see FIG. 1) to the opposite side of a combustion chamber 18, and has a shape conforming to the cam follower 34. The first inclined cam surface 35, the second inclined cam surface 36, the first concave groove 37, and the second concave groove 38 are provided on the lateral side of the convex portion 39 opposite to the cam follower 34. For this reason, a switching portion 33 of a thruster 11 is disposed at the same position as the cam follower 34 in the axial direction (the vertical direction in FIG. 21) of the cylinder.

The slider 92 includes a pressure receiving portion 97 (see FIGS. 21 and 23) and a transmitting portion 98 to regulate or control a swinging motion relative to the cam follower 34. The pressure receiving portion 97 contacts an intermediate portion 34 c (see FIG. 23) located between a swing end 34 b and the swing center of the cam follower 34 (the axis of the rocker shaft 6). The transmitting portion 98 contacts the other swing end 34 d (see FIG. 23) located on the opposite side of the swing end 34 b with respect to the swing center of the cam follower 34.

In the valve gear 91 for an engine according to the present preferred embodiment, since the switching portion 33 of the thruster 11 is provided at the same position as the cam follower 34 in the axial direction of the cylinder, a wide space in which to locate other elements is provided between the rocker arm 5 and the combustion chamber 18.

While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims. 

1-4. (canceled) 5: A valve gear for an engine comprising: a camshaft rotatably supported by a cylinder head; a first cam on the camshaft that drives one of an intake valve and an exhaust valve; a second cam on the camshaft spaced apart from the first cam in an axial direction, and that drives the other of the intake valve and the exhaust valve, the second cam including a cam profile different from a cam profile of the first cam; a synchronous cam on the camshaft that rotates in synchronism with the first cam and the second cam; a rocker shaft parallel or substantially parallel to the camshaft; a rocker arm supported by the rocker shaft to swing and move in the axial direction and to convert a rotation of one of the first cam and the second cam into a reciprocal motion and transmit the reciprocal motion to one of the intake valve and the exhaust valve; a cam follower swingably supported by the rocker shaft and that comes into contact with the synchronous cam; and a thruster that converts a swinging motion of the cam follower into a thrust in the axial direction and moves the rocker arm to one of a first side and a second side in the axial direction. 6: The valve gear for the engine according to claim 5, wherein the thruster includes: a slide portion that swings integrally with the cam follower and moves in the axial direction integrally with the rocker arm; and a switching portion supported by the cylinder head and including a first switch and a second switch, wherein the first switch and the second switch selectively come into contact with the slide portion; and the slide portion includes: a first inclined cam surface that receives a force at a first side thereof in the axial direction, wherein the force is generated by one of the first switch and the second switch in contact with the first inclined cam surface; and a second inclined cam surface that receives a force at a second side thereof in the axial direction, wherein the force is generated by the other of the first switch and the second switch in contact with the second inclined cam surface. 7: The valve gear for the engine according to claim 6, wherein the cam follower cannot move in the axial direction; and the slide portion is separate from the cam follower and is movable in the axial direction relative to the cam follower. 8: The valve gear for the engine according to claim 6, wherein each of the first switch and the second switch includes a pin that moves between an advancing position such that a first end of the pin comes into contact with the slide portion and a retreating position at which the first end of the pin separates from the slide portion; a second end of the pin abuts against a pin cam of a moving member that moves in a direction perpendicular or substantially perpendicular to a direction in which the pin moves; and the pin cam has a shape such that when the moving member moves to a first side, the first switch moves to the advancing position and the second switch moves to the retreating position, and when the moving member moves to a second side, the first switch moves to the retreating position and the second switch moves to the advancing position. 